Speed sensor and method for producing same

Abstract

A rotational speed sensor (10) comprising a shaft (54) having a reluctor (50) mounted thereon and coacting with a complementary shaped stator (18). The reluctor (50) and stator (18) have coacting regularly spaced projections (20, 58) which are magnetizable so that as the reluctor (50) rotates with the shaft (54), there is developed a cumulative voltage output which in turn enables utilization of much greater air gaps between the respective projections (20, 58). Because of the greater latitude in the air gaps, it is possible to construct a variable reluctance speed sensor (10) much more economically and with less emphasis on cumulative manufacturing tolerances. This greater flexibility of manufacturing with higher manufacturing tolerances contributes materially to the attainment of an economical and reliable speed sensor.

I claim: 
     
       1. A sensor for measuring rotational speed, comprising a nonmagnetic housing having a housing opening; means forming a stator received within said housing and including a base and a plurality of regularly spaced stator projections extending from said base axially along said housing; a winding-and-bobbin positioned within said housing and adjacent said base, a bobbin of said winding-and-bobbin having a bobbin opening; means forming an electrical connection with a winding of said bobbin; a magnet disposed at the geometric center line of said bobbin within said bobbin opening; means forming a cup which is disposed adjacent said magnet and opening toward the housing opening; a rotatable shaft having a boss at the end thereof proportioned to fit within said cup means; and a plurality of circumferentially spaced reluctor projections secured to said shaft, said reluctor projections complementary with said stator projections and positioned for rotation relative to said stator projections, the reluctor projections and stator projections being proportioned to permit at least limited axial and radial movement of said shaft and reluctor projections relative to said stator projections, such that rotation of said shaft brings the reluctor projections successively past the complementary spaced stator projections, into the spaced position between the stator projections, then past the next stator projections to develop a magnetic path comprising the magnet, cup means, air gap between said cup means and said boss, the reluctor projections, the air gaps between said reluctor projections and stator projections, the stator projections, and said stator, and magnetic flux lines are alternately diminished and enhanced between said spaced stator and spaced reluctor projections during shaft rotation to form an alternating voltage therebetween, whereby said alternative voltage having a frequency directly related to the rotational speed of said shaft. 
     
     
       2. The sensor in accordance with claim 1, including mounting ring means disposed at said housing opening for press fitting into a companion housing. 
     
     
       3. The sensor in accordance with claim 1, wherein the magnet comprises an annular magnet. 
     
     
       4. The sensor in accordance with claim 1, wherein said stator projections and reluctor projections are complementarily spaced so that said flux lines are simultaneously cut by each of the reluctor projections and stator projections during shaft rotation to provide a greater amplitude of output voltage.